Self-Assembly of AB Diblock Copolymer Confined in a Soft Nano-Droplet: A Combination Study by Monte Carlo Simulation and Experiment

The self-assembly of AB-type diblock copolymers confined in a three-dimensional (3D) soft nanodroplet is investigated by the combination of Monte Carlo simulation and experiment. The influences of two critical factors, i.e., confinement degree of the imposed confinement space and the interfacial interaction between each individual block and boundary interface, on the 3D soft confined self-assembly are examined systematically. The simulation results reveal that block copolymer chains become more and more folded as the confinement degree (it can be monitored by the ratio of <i>D</i>/<i>L</i>, where <i>L</i> is the length of polymer chain and <i>D</i> is the reduced diameter of the final polymeric particle) is enhanced, causing a series of morphological transitions. Based on the simulation prediction, we perform the corresponding experiments by the 3D confined self-assembly of both symmetric and asymmetric block copolymers within the emulsion droplets. The experimental results well reproduce the confinement degree induced morphological transitions predicted by the simulations, such as the transition from segmented pupa-like particle to hamburger particle and the transition from raspberry-like particle to triangle-like particle, and then to hamburger particle. The current study implies that self-assembled nanostructures under 3D soft confinement can be simply controlled by tuning the confinement degree and interfacial property, i.e., the ratio of <i>D</i>/<i>L</i> and the interfacial interaction between each individual block and boundary interface

Online Rheological Investigation on Ion-Induced Micelle Transition for Amphiphilic Polystyrene-<i>block</i>-Poly(acrylic acid) Diblock Copolymer in Dilute Solution

The ion-induced micellar transition is online-investigated by the time dependence of the viscosity of the solution under shear flow for the first time. During the morphological transition, the change in the micellar structure can be tracked by the change in viscosity. Adding HCl or CaCl₂ into pre-prepared spherical micelle solution from the self-assembly of polystyrene-<i>block</i>-poly­(acrylic acid) (PS₁₄₄-<i>b</i>-PAA₂₂) in the <i>N</i>,<i>N</i>-dimethylformamide (DMF)/water mixture, the micellar structures change into short cylinders, long, entangled cylinders, and then lamellae or vesicles, corresponding to the viscosity increasing first and then declining. When HCl or CaCl₂ is added to the pre-prepared spherical micelle solution formed by PS₁₄₄-<i>b</i>-PAA₅₀ in the dioxane/water mixture, the micellar structures are quickly transformed into cylinders or lamellae before carrying out the rheological measurement and then are turned to vesicles or spheres under the shearing, corresponding to a gradual decline in viscosity. This study shows that the rheology can be a very simple and effective online method on the investigation of the micellization, which plays an important role in understanding the micellization mechanism and micellar transition pathway of block copolymers in dilute solution

Controllable Location of Inorganic Nanoparticles on Block Copolymer Self-Assembled Scaffolds by Tailoring the Entropy and Enthalpy Contributions

Precisely controlling the spatial location and alignment of functional nanoparticles (NPs) on polymeric scaffolds is of great importance to not only create novel nanostructures but also enhance the properties of the hybrid nanomaterials. Herein, we demonstrate a strategy of tailoring the entropic and enthalpic contributions to precisely position gold nanoparticles (AuNPs) on block copolymer (BCP) scaffolds through the confined coassembly of BCPs and AuNPs within the emulsion droplet. According to this strategy, entropic effect arisen by the loss in conformational entropy and the enthalpic attraction between ligands on AuNPs and surfactants at the oil/water interface induce the solid AuNPs to move to the BCP surface, while the enthalpic interaction between the ligands on AuNPs and the corresponding polymer chains guides the AuNPs to position at the appropriate place. By this strategy, both the location and alignment of AuNPs on BCP scaffolds can be controlled at will, such as at the two terminals or along the lamellar boundary of the pupa-like scaffolds, or at the bases of pinecone-like or bud-like scaffolds, or at the head of one hemisphere, the entire hemisphere, or along the boundary between the two distinct hemispheres of the Janus-like scaffolds. We believe that this methodology can offer a universal route to achieve the precise positioning of functional NPs on the BCP scaffolds

Inorganic Nanoparticle Induced Morphological Transition for Confined Self-Assembly of Block Copolymers within Emulsion Droplets

Recently, it has been reported that the incorporation of functional inorganic nanoparticles (NPs) into the three-dimensional (3D) confined self-assembly of block copolymers (BCPs) creates the unique nanostructured hybrid composites, which can not only introduce new functions to BCPs but also induce some interesting morphological transitions of BCPs. In the current study, we systematically investigate the cooperative self-assembly of a series of size-controlled and surface chemistry-tunable gold nanoparticles (AuNPs) and polystyrene-<i>b</i>-poly­(2-vinylpyridine) (PS-<i>b</i>-P2VP) diblock copolymer within the emulsion droplets. The influences of the size, content, and surface chemistry of the AuNPs on the coassembled nanostructures as well as the spatial distribution of AuNPs in the hybrid particles are examined. It is found that the size and content of the AuNPs are related to the entropic interaction, while the surface chemistry of AuNPs is related to the enthalpic interaction, which can be utilized to tailor the self-assembled morphologies of block copolymer confined in the emulsion droplets. As the content of PS-coated AuNPs increases, the morphology of the resulting AuNPs/PS-<i>b</i>-P2VP hybrid particles changes from the pupa-like particles to the bud-like particles and then to the onion-like particles. However, a unique morphological transition from the pupa-like particles to the mushroom-like particles is observed as the content of P4VP-coated AuNPs increases. More interestingly, it is observed that the large AuNPs are expelled to the surface of the BCP particles to reduce the loss in the conformational entropy of the block segment, which can arrange into the strings of necklaces on the surfaces of the hybrid particles

Gold-Catalyzed [4 + 1] Heterocyclization of Hydroxamic Acid and Nonactivated Alkyne: A Protocol to Construct 5‑Methyl-1,4,2-dioxazole

A novel gold-catalyzed [4 + 1] heterocyclization of nonactivated alkyne and hydroxamic acid is developed for the regiospecific synthesis of 5-methyl-1,4,2-dioxazole, which is an important structural motif in various bioactive molecules. The current methodology is characterized by high efficiency, simple operation, mild reaction conditions, and good functional group compatibility. Moreover, gram-scale synthesis and synthetic application toward bioactive molecular skeletons have been realized

Entropy-Driven Hierarchical Nanostructures from Cooperative Self-Assembly of Gold Nanoparticles/Block Copolymers under Three-Dimensional Confinement

The cooperative self-assembly of polystyrene-<i>b</i>-poly­(4-vinylpyridine) block copolymers (BCPs) and gold nanoparticles (AuNPs) confined within the emulsion droplets is studied by combining both the experiments and Monte Carlo simulations. The results indicate that the entropic interaction between the AuNPs and BCP domain is a critical parameter to dominate the spatial arrangement of AuNPs and the nanostructure of the hybrid nanoparticles, which can be utilized to design novel hierarchical hybrid nanoparticles. Based on this theoretical observation, a large number of unique Janus hybrid nanoparticles, including pupa-like nanoparticles with AuNPs concentrated at one pole of the particles, spherical nanoparticles with AuNPs enriched in a bulge on the sphere surface, and the gourd-like, clover-like, and four-leaf-clover-like nanoparticles from the further hierarchical assembly of small hybrid Janus nanoparticles, are fabricated via three-dimensional (3D) confined self-assembly

Synthesis of Novel Two-Phase Co@SiO₂ Nanorattles with High Catalytic Activity

Noble metal nanocatalysts with remarkable catalytic properties have attracted much attention; however, the high cost of these materials limits their industrial applications. Here, we design and prepare Co@SiO₂ nanorattles as a mixture of hcp-Co and fcc-Co phases as a substitute. The nanorattles exhibit both superior catalytic activity and high stability for the reduction of <i>p</i>-nitrophenol. The reduction rate nearly follows pseudo-first-order kinetics, and the reaction rate constant is as high as 0.815 min^–1 and is maintained at 0.565 min^–1 even after storing for one month, which is higher than that reported for noble metal nanocatalysts. Such an excellent property can be attributed to the novel two-phase composition and rattle-type structure

Size- and Shape-Dependent Photoexcitation Electron Transfer in Metal Nanoclusters

There are some unresolved fundamental issues for metal nanoclusters; for instance, the close-packed structure transformation from face-centered cubic (fcc) to hexagonal close-packed (hcp) has not yet been reported, and photoexcitation electron transfer is not well understood. Herein, we realized for the first time the fcc-to-hcp structure transformation and revealed the size- and shape-dependent photoexcitation electron transfer for metal nanoclusters. Specifically, a thermally induced ligand exchange method was developed, and a rod-shaped hcp Au42(SCH2Ph)32 (HSCH2Ph: benzyl mercaptan) with the largest aspect ratio was synthesized from fcc Au28(SPh-tBu)20 (HSPh-tBu: p-tert-butylphenol) and structurally resolved, which shows a sharp absorption at 815 nm and dual emission that is well interpreted by time-dependent density functional theory (TD-DFT) calculations. The structure transformation pathway was proposed, and a novel, rod-shaped hcp Au58(SR)40 with larger aspect ratio was predicted. Interestingly, it is found that the kernel-based middle-to-both ends sp ← sp photoexcitation electron transfer can be extended to other rod-like (one-dimensional) gold nanoclusters, and the major photoexcitation turns to the kernel-based sp ← sp transition from the staple-to-kernel sp ← d transition when the spherical gold nanocluster size is increased to Au42 and the Au(6sp) composition increases with increasing size for structure-similar nanoclusters. These findings deepen our understanding of metal nanocluster photoexcitation electron transfer and provide guidance for future nanocluster property tuning aimed at practical applications

Size- and Shape-Dependent Photoexcitation Electron Transfer in Metal Nanoclusters

There are some unresolved fundamental issues for metal nanoclusters; for instance, the close-packed structure transformation from face-centered cubic (fcc) to hexagonal close-packed (hcp) has not yet been reported, and photoexcitation electron transfer is not well understood. Herein, we realized for the first time the fcc-to-hcp structure transformation and revealed the size- and shape-dependent photoexcitation electron transfer for metal nanoclusters. Specifically, a thermally induced ligand exchange method was developed, and a rod-shaped hcp Au42(SCH2Ph)32 (HSCH2Ph: benzyl mercaptan) with the largest aspect ratio was synthesized from fcc Au28(SPh-tBu)20 (HSPh-tBu: p-tert-butylphenol) and structurally resolved, which shows a sharp absorption at 815 nm and dual emission that is well interpreted by time-dependent density functional theory (TD-DFT) calculations. The structure transformation pathway was proposed, and a novel, rod-shaped hcp Au58(SR)40 with larger aspect ratio was predicted. Interestingly, it is found that the kernel-based middle-to-both ends sp ← sp photoexcitation electron transfer can be extended to other rod-like (one-dimensional) gold nanoclusters, and the major photoexcitation turns to the kernel-based sp ← sp transition from the staple-to-kernel sp ← d transition when the spherical gold nanocluster size is increased to Au42 and the Au(6sp) composition increases with increasing size for structure-similar nanoclusters. These findings deepen our understanding of metal nanocluster photoexcitation electron transfer and provide guidance for future nanocluster property tuning aimed at practical applications

Co₃O₄ Nanocages for High-Performance Anode Material in Lithium-Ion Batteries

Co₃O₄ nanoparticles have been prepared by a facile strategy, which involves the thermal decomposition of nanoparticles of cobalt-based Prussian blue analogues at different temperatures. The nanoparticles prepared at 450, 550, 650, 750, and 850 °C exhibited a high discharge capacity of 800, 970, 828, 854, and 651 mAhg^–1, respectively, after 30 cycles at a current density of 50 mAg^–1. The nanocages produced at 550 °C show the highest lithium storage capacity. It is found that the nanocages display nanosize grains, hollow structure, a porous shell, and large specific surface area. At the temperature higher than 650 °C, the samples with larger grains, better crystallinity, and lower specific surface area can be obtained. It is found that the size, crystallinity, and morphology of nanoparticles have different effects on electrochemical performance. Better crystallinity is able to enhance the initial discharge capacity, while porous structure can reduce the irreversible loss. Therefore, the optimal size, crystallinity, and cage morphology are suggested to be responsible for the improved lithium storage capacity of the sample prepared at 550 °C. The as-prepared Co₃O₄ nanoparticles also have a potential application as anode material for Li-ion batteries due to their simple synthesis method and large capacity